This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-192841, filed Jun. 27, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a press forming machine for optical devices which manufactures a glass optical device such as an optical lens or a prism by press forming.
In a press forming machine for a glass optical device, a die and a glass material are heated and press forming of the glass material is then carried out by using the die. Methods generally used for heating the die and the glass material can be roughly classified into two types. One type is high-frequency induction heating and disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication Nos. 64-45734 and 63-170228. The other type is radiant heating using an infrared lamp and disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 5-186230.
Of these types of method, high-frequency induction heating has a problem in depth of penetration of the high-frequency and it is difficult to evenly heat a metal portion of the die. On the contrary, radiant heating using an infrared lamp can readily realize the even temperature distribution and is suitable for press-forming an optical device having the high accuracy.
FIG. 3 shows an outline (cross-sectional view in a lateral direction) of an infrared lamp unit used in a press forming machine disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-186230. This infrared lamp unit 43 is constituted by forming a substantially annular sub unit by combining two pairs of a semi-arc infrared lamp 41 and a reflecting mirror 42 and superimposing a plurality of the sub units in the vertical direction.
When the infrared lamp unit 43 is constituted in this manner, a gap is formed at an opposed portion of the infrared lamp 41 in the circumferential direction as indicated by an arrow Z in FIG. 3. In case of press-forming a typical optical device, the sufficient accuracy of form can be obtained even if such an infrared lamp unit 43 is used. If the higher accuracy of form is demanded, however, astigmatism of a press-formed product caused due to the temperature distribution in the circumferential direction becomes a problem. Further, the casing of the infrared lamp must be processed into a semi-circular shape, which leads to increase in cost for manufacturing the lamp unit.
The present invention has been made in view of the above-described problems of the conventional heating methods in the press forming machine for a glass optical device. It is an object of the present invention to provide a press forming machine which is superior in the temperature uniformity of a die to be heated and has a manufacturing cost lower than that of a machine using a conventional arc infrared lamp unit.
According to the present invention, there is provided a press forming machine for a glass optical device, comprising:
a pair of upper and lower dies for press-forming a glass material; and
an infrared lamp unit which is arranged around the dies and heats the dies and the glass material; wherein
the infrared lamp unit is constituted by straight tube type infrared lamps, and each of the infrared lamp has a vertical axis and is arranged around the dies in the circumferential direction.
According to the press forming machine for a glass optical device of the present invention, since the infrared lamp unit is constituted by arranging a plurality of the straight tube type infrared lamps in the above-described manner, it is superior to a conventional infrared lamp unit constituted by combining semi-circular infrared lamps in the temperature uniformity in the circumferential direction of the dies to be heated. As a result, it is possible to manufacture a glass optical device having the high accuracy of form. Further, since the straight tube type infrared lamp is used, the manufacturing cost can be lower than that of the conventional semi-circular infrared lamp.
Preferably, in the press forming machine for a glass optical device according to the present invention, in order to cool down a terminal portion of the straight tube type infrared lamp, a nozzle for directly blasting air or an inert gas to the terminal portion is provided.
Preferably, dimples are formed on an casing of the straight tube type infrared lamp. Consequently, slack of filaments can be avoided at the time of heating, thereby extending the life duration of the infrared lamp.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.